I've often heard it said, by many audio writers I trust, that very small level differences [on the order a 1 dB or even less] are often (if not usually) perceived as quality differences by humans, and not simply level differences. I've always accepted this without question, however in arguing with others in other forums, I need documentation to back this. What I'm asking for people's help with is in finding the original work(s) which demonstrated this, in the form of a scholarly paper(s). Anyone?